Typically, systems of automatic storage and retrieval of inventory items are used in warehouse applications. All storage and retrieval systems attempt to reduce the time taken in placing inventory items in storage and to reduce the time taken in retrieving the inventory items from storage when desired. Small parts frequently cannot be palletized and often must be stored in bins or containers because of their size or delicate construction. Conventional storage and retrieval systems use solid storage shelves whereby an extractor or picking mechanism must go to the shelf to pick the desired inventory item. This limits the conventional system to essentially one transaction each time the extractor is operated and is not suited for placement in the middle of a high speed production line.
Efficient operation of a manufacturing facility requires that the upstream machinery continue to operate without interruption even though the downstream machinery may be experiencing down time. It is undesirable to stop and start the upstream machinery, because restarting the machine may be difficult, or for efficiency it may be desired to finish a production run. In addition, continuous operation will produce more product, since the down time for each machine will not be linked to, or added to, down time for other units.
In the past, upstream machines and other downstream machines have been linked close together requiring both machines to stop when either one does. In an attempt to provide some accumulation the operations have been spaced apart with the connecting conveyor providing brief accumulations. Thus, if operation of the downstream machine is interrupted, the upstream machine will merely add additional objects to the conveyor until the downstream machine is repaired. In some instances, serpentine conveyor paths have been used to receive products continuously from the upstream operation. Continuously adding more products to a serpentine conveyor which is not feeding to the downstream unit causes a continuous build-up of products on the conveyor and any associated problems that the build-up of products may entail. In addition, if the downstream unit is operating, the increased length of the serpentine conveyor path creates a delay between discharge from the upstream machine to receipt by the downstream machine.
One method has been proposed for accommodating a collection of articles being produced upstream, while the downstream processing unit is not in operation. These devices, generally called accumulators, are designed to pick up the articles which pass along a conveyor by lifting the edges which extend over the sides of the conveyor. This type of accumulator is generally used for objects which are flat and relatively long and wide compared to the height. These devices are typically limited in their capacity of accumulating objects by the vertical lift limit, typically the ceiling height in the assembly room, and therefore actual accumulation is limited to a relatively small number of objects.